This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The toxicity of arsenic is dependent upon not only exposure but also upon its speciation upon consumption. Variations within this speciation may profoundly affect the toxic and genotoxoic effects of arsenicals. Monitoring the effects of toxic arsenic interactions within the body would provide powerful biomarkers, not only of the exposure itself but the biochemical impact of the exposure. The hypothesis to be tested is that reaction between mitochondrial proteins and arsenic are responsible for the generation of oxidative stress. We are monitoring the interactions of inorganic arsenic and of synthetic analogues of the organic arsenic species that are formed upon metabolism of arsenic with proteins of the mitochondrial proteome. Electrospray quadrupole time-of-flight mass spectrometry is being used to definitively establish a site or sites of arsenic binding and enzyme inhibition. These interactions mechanistically characterize the mitochondrial induction of oxidative stress by arsenic and serve to direct the further biomarker isolation studies. We have also established speciation protocols for the simultaneous detection of multiple arsenic species in biological tissues by high resolution inductively coupled mass spectrometry. These studies are being conducted in FVB/n and transgenic Tg.AC mice to understand the transport and speciation in different tissues with regard to oxidative stress generated at those sites.